Thermoelectric materials and related compositions and methods

ABSTRACT

A thermoelectric material includes a polymer matrix and a plurality of partially coated particles dispersed within the polymer matrix. Each particle of the plurality has a discontinuous coating of metal on a carbon-based material. A method includes dispersing functionalized particles comprising a carbon-based material in a solvent; providing a metal salt in the solvent; and forming a plurality of distinct metal volumes on a surface of the functionalized particles to form partially coated particles. The distinct metal volumes are thermally insulated from other volumes of the plurality. A composition of matter includes a discontinuous coating of metal on a surface of a carbon-based material. The carbon-based material is selected from the group consisting of graphene oxide and functionalized carbon nanotubes.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.15/586,945, filed May 4, 2017, pending, the disclosure of which ishereby incorporated herein in its entirety by this reference.

TECHNICAL FIELD

Embodiments of the present disclosure relate generally to materialsexhibiting thermoelectric properties and methods and compositionsrelated to such materials.

BACKGROUND

Thermoelectric materials are materials that change temperature when anelectric current is passed through them. Thermoelectric materials may beformed from a variety of semiconductor materials, and may becharacterized in terms of the material's thermoelectric efficiency ZT or“figure of merit” at a temperature, which is defined by the relation:

${{ZT} = {\frac{S^{2}\sigma}{k}T}},$

Where S is the material's Seebeck coefficient; σ is the material'selectrical conductivity; k is the material's thermal conductivity; and Tis the temperature. The Seebeck coefficient is approximated as a voltagedifference between two ends of a sample of thermoelectric materialdivided by a temperature difference between the two ends:

$S = {\frac{\Delta \; V}{\Delta \; T}.}$

High Seebeck coefficients and electrical conductivity, coupled with lowthermal conductivity, yield a high thermoelectric efficiency.Unfortunately, in many conventional thermoelectric materials, increasesin Seebeck coefficient are associated with reduction in electricalconductivity and vice versa. Furthermore, electrical and thermalconductivity tend to be positively correlated, making it difficult tofind materials having both a high electrical conductivity and a lowthermal conductivity.

In underground drilling applications, such as oil and gas or geothermaldrilling, a borehole is drilled through a subterranean formation, oftendeep into the earth. Such bore holes are drilled or formed by a drillbit connected to the end of a series of sections of drill pipe, so as toform an assembly commonly referred to as a “drill string.” The drillstring extends from the surface to the bottom of the borehole. As thedrill bit rotates under an applied axial force, commonly termed “weighton bit,” it advances into the earth, thereby forming the borehole. Inorder to lubricate the drill bit and flush cuttings from the drill bit'spath as it advances, a high pressure solids-laden fluid, referred to as“drilling mud,” is directed through an internal passage in the drillstring and out through the drill bit. The drilling mud then flows to thesurface through an annular passage formed between the exterior of thedrill string and the surface or interior wall of the bore hole.

The distal or bottom end of the drill string, which includes the drillbit, is referred to as a “downhole assembly.” In addition to the drillbit, the downhole assembly often includes specialized modules or toolswithin the drill string that make up an electrical system for the drillstring. Such modules often include sensing modules. In manyapplications, the sensing modules provide the drill string operator withinformation regarding the formation as it is being drilled through,using techniques commonly referred to as “measurement while drilling”(MWD) or “logging while drilling” (LWD). For example, resistivitysensors may be used to transmit and receive high frequency signals(e.g., electromagnetic waves) that travel through the formationsurrounding the sensor.

As can be readily appreciated, such an electrical system may includemany sophisticated electronic components, such as the sensorsthemselves, which in many cases include printed circuit boards.Additional associated components for storing and processing data in thecontrol module may also be included on the printed circuit boards.Unfortunately, many of these electronic components generate heat. Evenif the electronic component itself does not generate heat, thetemperature of the formation itself, particularly in deep boreholes andin geothermal wells, may exceed the maximum temperature capability ofthe components (which may be about 150° C.

Overheating downhole frequently results in failure or reduced lifeexpectancy for thermally stressed electronic components. Consequently,cooling of the electronic components can be important. Unfortunately,cooling is made difficult by the fact that the temperature of theformation surrounding deep wells, especially geothermal wells, istypically relatively high, and may exceed 200° C.

Downhole tools are exposed to tremendous thermal strain. The metaldownhole tool housing is in direct thermal contact with the boreholedrilling fluids and conducts heat from the borehole drilling fluid intothe downhole tool housing. Conduction of heat into the tool housingraises the ambient temperature inside of the electronics chamber. Thus,the thermal load on a non-insulated downhole tool's electronic system isenormous and can lead to electronic failure. Electronic failure is timeconsuming and expensive. In the event of electronic failure, downholeoperations must be interrupted while the downhole tool is removed fromdeployment and repaired.

BRIEF SUMMARY

In some embodiments, thermoelectric material includes a polymer matrixand a plurality of partially coated particles dispersed within thepolymer matrix. Each particle of the plurality has a discontinuouscoating of metal on a carbon-based material.

A method includes dispersing functionalized particles comprising acarbon-based material in a solvent; providing a metal salt in thesolvent; and forming a plurality of distinct metal volumes on a surfaceof the functionalized particles to form partially coated particles. Thedistinct metal volumes are thermally insulated from other volumes of theplurality.

A composition of matter includes a discontinuous coating of metal on asurface of a carbon-based material. The carbon-based material isselected from the group consisting of graphene oxide and functionalizedcarbon nanotubes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified cross-sectional side view illustrating anembodiment of a thermoelectric material according to the presentdisclosure.

FIG. 2 is a simplified diagram illustrating a molecular structure ofsome particles disclosed herein.

FIGS. 3 and 4 are simplified diagrams illustrating molecular structuresof materials that may be used to form the particles shown in FIG. 2.

FIG. 5 is a simplified diagram illustrating an earth formation in whicha tool having a thermoelectric material may be used.

FIG. 6 is a simplified diagram illustrating the tool of FIG. 5 in moredetail.

DETAILED DESCRIPTION

The illustrations presented herein are not actual views of anyparticular material, but are merely idealized representations that areemployed to describe example embodiments of the present disclosure.Additionally, elements common between figures may retain the samenumerical designation.

FIG. 1 illustrates a thermoelectric material 100 having a polymer matrix102 and a plurality of partially coated particles 104 dispersed withinthe polymer matrix 102.

The polymer matrix 102 may be a material such as polyether ether ketone(PEEK), polyethylene (PE), polyethylene terephthalate (PET), polyvinylchloride (PVC), polyurethane (PU), poly(methyl methacylate) (PMMA),etc., which may be selected based on density, thermal conductivity,method of curing, etc.

Each of the partially coated particles 104 may have a discontinuouscoating of metal over a carbon-based material. For example, as shown inFIG. 2, the partially coated particles 104 may include graphene oxide114. The graphene oxide 114 may have a metal 116 formed over portions ofthe graphene oxide 114. The metal 116 may include any metal formulatedto conduct heat, such as nickel, cobalt, copper, silver, platinum,palladium, chromium, tantalum, antimony, iron, tin, gold, etc., andalloys and combinations thereof. The portions of the metal 116 may bethermally insulated from one another. That is, there may be nometal-to-metal contact between distinct portions of the metal 116, buteach portion of the metal 116 may be electrically connected to othersvia the graphene oxide 114 on which the metal 116 is disposed. Becausethe portions of the metal 116 do not contact other portions of the metal116, heat may not tend to flow easily from one disconnected portion ofthe metal 116 to another. Therefore, the partially coated particles 104may have relatively lower thermal conductivity than similar particlesentirely coated with metal.

Because the portions of the metal 116 are electrically connected toother portions of the metal 116 via the graphene oxide 114, electronsmay tend to flow easily from one disconnected portion of the metal 116to another. Therefore, the partially coated particles 104 may haverelatively high electrical conductivity, which may be similar to theelectrical conductivity of particles entirely coated with metal.

As another example, the partially coated particles 104 may includefunctionalized carbon nanotubes. In other embodiments, the partiallycoated particles 104 may include any other carbon-containing material,such as nanodiamond, amorphous carbon, carbon black,buckminsterfullerenes, etc. Whatever the carbon form, a metal 116 mayformed over portions thereof.

The partially coated particles 104 may have an average largest lineardimension from about 1 nm to about 500 μm, such as from about 10 nm toabout 50 μm, or from about 50 nm to about 10 μm. The disconnectedportions of the metal 116 may have an average largest linear dimensionfrom about 0.1 nm to about 500 nm, such as from about 0.5 nm to about100 nm, or from about 1 nm to about 50 nm. The partially coatedparticles 104 may be from about 0.1% to about 20% volume of thethermoelectric material 100, such as from about 0.5% to about 10%, orfrom about 1% to about 5%.

To form the partially coated particles 104 (FIG. 1), functionalizedcarbon-based particles may be dispersed in a solvent, a metal salt maybe provided in the solvent, and distinct portions of the metal 116 (FIG.2) may be formed on a surface of the functionalized carbon-basedparticles.

FIG. 3 illustrates a sheet of graphene oxide 130. The graphene oxide 130includes a sheet of carbon atoms generally bonded to other carbon atomsin a structure of interlocking rings. Though shown and described as a“sheet,” the graphene oxide 130 need not be planar. Graphene oxide isdescribed generally in U.S. Pat. No. 8,871,821, “Graphene and GrapheneOxide Aerogels,” issued Oct. 28, 2014, the entire disclosure of which ishereby incorporated herein by this reference. As illustrated in FIG. 3,the graphene oxide 130 may include hydroxyl groups (—OH), carboxylgroups (—COOH) and/or epoxy groups (—O—), or any other oxygen-containingfunctionalization. The functionalization on the graphene oxide 130 maybe on some but not all of the carbon atoms. In general, the carbon atomsthat are functionalized may be those to which metal 116 (FIG. 2) will besubsequently attached. Therefore, to form a partial coating havingdistinct portions of the metal 116, the graphene oxide 130 may havedistinct areas that are functionalized, and other areas that are notfunctionalized.

The functionalized carbon-based particles may be dispersed in a solvent,such as water (e.g., deionized water), an acid, a base, an organicsolvent, etc. Due to the presence of hydroxyl groups, carboxyl groups,and/or epoxy groups, the functionalized carbon-based particles maydisperse relatively easily in aqueous solutions. The solvent may bestirred or otherwise mixed to suspend the functionalized carbon-basedparticles throughout the solvent. In some embodiments, the solvent maybe subjected to ultrasonic energy to enhance dispersion of thefunctionalized carbon-based particles.

The solvent may be provided with a metal salt, which may be added beforeor after the functionalized carbon-based particles are dispersed. Insome embodiments, the metal salt is dissolved in the solvent prior toadding the functionalized carbon-based particles. In other embodiments,the metal salt may be added after the functionalized carbon-basedparticles are mixed with the solvent. The metal salt may be dissolved orsuspended in the solvent. The metal salt may be any metal saltcontaining the metal to be deposited, such as nitrates, sulfides,sulfates, sulfites, chlorides, bromides, chlorates, perchlorates,phosphates, etc. For example, the metal salt may be NiCl₂, NiSO₄, CoCl₂,CoSO₄, Cu(NO₃)₂, AgNO₃, AgCl, etc. The metal salt may selected based inpart on its solubility in the solvent.

Metal cations from the metal salt may react with, be attracted to,adsorbed to, or be weakly bound to functional groups on thefunctionalized carbon-based particles. For example, if thefunctionalized carbon-based particles are graphene oxide 130, as shownin FIG. 3, metal cations from the metal salt may be attracted to thefunctionalized areas. FIG. 4 illustrates the attraction of metal cations142 (Ni²⁺) to the functional groups of the graphene oxide 130. The metalcations 142 may be attracted to some or all of the functional groups onthe graphene oxide 130.

The metal cations 142 may form distinct volumes of metal on the surfaceof the functionalized carbon-based particles (e.g., the graphene oxide130). For example, the metal cations 142 may be reduced, such as fromNi⁺ to Ni, Cu²⁺ to Cu, Ag⁺ to Ag, or Co²⁺ to Co. In some embodiments,the metal cations 142 may be reduced and deposited by electrolessdeposition, reaction with a reducing agent, etc. Electroless depositionmethods are described in U.S. Patent Application Publication2016/0083860, “Methods of Coating Substrates with Composite Coatings ofDiamond Nanoparticles and Metal,” published Sep. 18, 2014, the entiredisclosure of which is hereby incorporated by this reference. Forexample, the metal cations 142 may react with a hypophosphate or withsodium borohydrite. In some embodiments, metal cations 142 may bereduced by high temperature reduction, ultraviolet assistedphotocatalytic reduction, or chemical reduction.

The solvent may be removed from the partially coated particles 104concurrently with or after deposition of the metal 116 on the partiallycoated particles 104. For example, the solvent may be removed byevaporation, filtration, etc., or by combinations of separationtechniques. Once separated, the resulting partially coated particles 104may be in the form of a powder, or may be processed to form a powder(e.g., by milling or grinding). The partially coated particles 104 maythen be mixed with the polymer matrix 102 or a precursor thereof to formthe thermoelectric material 100 shown in FIG. 1. The polymer matrix 102may be formed into a selected shape (e.g., molded, extruded, cut, etc.)and may be cured to form the thermoelectric material 100 into a masshaving selected properties.

Though the partially coated particles 104 are shown and described inFIGS. 2-4 as being graphene oxide, the partially coated particles 104may also include other forms of carbon. In particular, carboxylatedcarbon nanotubes may be conceptualized as rolled graphene oxide sheets,and may therefore be processed in a similar manner. Othercarbon-containing particles may also be used. Without being bound to anyparticular theory, it appears that materials having oxygen-abundantfunctional groups may be useful for the materials and methods describedherein, due to their cation exchange and interaction capacities.

The carbon can be used as a host material to incorporate metallicnanoscale (largest diameter less than 1 μm) and microscale (largestdiameter less than 500 μm) particles. Again without being bound to anyparticular theory, it appears that the presence of a large number offunctional groups (hydroxyl, carboxyl, epoxy, etc.) decreases theability of the particles to transfer electrons.

The partially coated particles 104 can effectively be used as athermoelectric material because of several advantages. First, thenon-connected portions of the metal 116 cause low or modest thermalconductivity in comparison to metals or fully metal-coated particles.Second, the partially coated particles 104 may have relatively highelectrical conductivity due to electron transport between highlyconductive metal 116 through the underlying carbon particle (e.g., thegraphene sheet) if the particle is electrically conductive. Finally,when the partially coated particles 104 are embedded into a polymermatrix, the material may have a high Seebeck (or thermoelectric)coefficient.

For example, the thermoelectric material 100 may have a thermalconductivity of less than about 10⁻² mW/cm K, less than about 10⁻³mW/cm·K, or even less than about 10⁻⁴ mW/cm K. The thermoelectricmaterial 100 may have an electrical conductivity of at least about 0.005S/cm, at least about 0.007 S/cm, at least about 0.01 S/cm, or even atleast about 0.02 S/cm. The thermoelectric material 100 disclosed hereinmay have a Seebeck coefficient of at least about 1000 μV/K, at leastabout 1500 μV/K, at least about 2000 μV/K, or even at least about 3000μV/K.

Thermoelectric materials 100 as described herein may be used for a widevariety of applications. For example, thermoelectric materials 100 maybe used in downhole tools to manage heat flow and protect electronicdevices. Such uses are described further in U.S. Patent ApplicationPublication 2008/0277162, “System and Method for Controlling Heat Flowin a Downhole Tool,” published Nov. 13, 2008, the entire disclosure ofwhich is incorporated herein by this reference.

For example, and as shown schematically in FIG. 5, a well bore 201 mayextend into an earth formation, into which a logging tool includingsensors and electronics has been lowered. The well bore 201 extends intoan earth formation 203, which includes various layers. A tool 209 (whichmay be a cutting tool, a logging tool, etc.) having sensors andelectronics 219 has been lowered into the well bore 201 via a wire line211. The surface equipment 222 includes an electric power supply toprovide electric power and a signal processor to receive and processelectric signals from the sensors and electronics 219. Alternatively, apower supply and signal processor are located in the tool 209. In thecase of the wire line deployment, the wire line 211 may be utilized forprovision of power and data transmission.

FIG. 6 illustrates that the tool 209 may include a thermoelectric device223 (which may include the thermoelectric material 100 shown in FIG. 1).The electronics 219 may act as a heat source. Heat 225 may flow from theelectronics 219 to the thermoelectric device 223 or vice versa tomaintain the electronics 219 at a constant temperature. Thethermoelectric device 223 may be electrically connected to a powersource (e.g., the wire line 211 or a battery), which may drive thethermoelectric device 223 to transfer heat 225 from the electronics 219.Because the tool 209 may be used in harsh environments, thethermoelectric device 223 may be beneficial for increasing the usefullife of the electronics 219. For example, the electronics 219 may bemaintained at a temperature of about 150° C. or less.

Thermoelectric materials 100 may be formed in any selected size andshape, and therefore may be useful for a wide variety of applications inwhich conventional heat transfer devices are not suitable. For example,the thermoelectric material 100 may be formed in a sheet and wrappedaround a sensitive component. In some embodiments, the thermoelectricmaterial 100 may be placed on an inside wall of a body in which asensitive component is placed. For example, the thermoelectric material100 may be placed inside a tool body, and may help to maintain atemperature inside the tool body where electronics are located, even ifthe thermoelectric material 100 does not contact the electronics.

As another example, thermoelectric materials 100 may be used to controlthe temperature of electronic components (e.g., lasers, processors,memory, storage, etc.) for any application, such as laboratoryequipment, computers, consumer electronics, etc. Thermoelectricmaterials 100 may also be used for cryogenic applications. In someembodiments, thermoelectric materials 100 may be used for powergeneration, such as in downhole devices.

Additional non limiting example embodiments of the disclosure aredescribed below.

Embodiment 1

A thermoelectric material comprising a polymer matrix and a plurality ofpartially coated particles dispersed within the polymer matrix. Eachparticle of the plurality has a discontinuous coating of metal on acarbon-based material.

Embodiment 2

The thermoelectric material of Embodiment 1, wherein the discontinuouscoating of metal comprises a metal selected from the group consisting ofnickel, cobalt, copper, silver, platinum, palladium, chromium, tantalum,antimony, iron, tin, and gold.

Embodiment 3

The thermoelectric material of Embodiment 2, wherein the discontinuouscoating of metal comprises a metal selected from the group consisting ofnickel, cobalt, copper, and silver.

Embodiment 4

The thermoelectric material of any of Embodiments 1 through 3, whereinthe plurality of partially coated particles comprises graphene oxide.

Embodiment 5

The thermoelectric material of any of Embodiments 1 through 4, whereinthe plurality of partially coated particles comprises functionalizedcarbon nanotubes.

Embodiment 6

The thermoelectric material of any of Embodiments 1 through 5, whereinthe polymer matrix comprises at least one material selected from thegroup consisting of polyether ether ketone (PEEK), polyethylene (PE),polyethylene terephthalate (PET), polyvinyl chloride (PVC), polyurethane(PU), and poly(methyl methacylate) (PMMA).

Embodiment 7

The thermoelectric material of any of Embodiments 1 through 6, whereinthe thermoelectric material exhibits a figure of merit of at least 0.9.

Embodiment 8

A method comprising dispersing functionalized particles comprising acarbon-based material in a solvent; providing a metal salt in thesolvent; and forming a plurality of distinct metal volumes on a surfaceof the functionalized particles to form partially coated particles. Thedistinct metal volumes are thermally insulated from other volumes of theplurality.

Embodiment 9

The method of Embodiment 8, further comprising dispersing the partiallycoated particles within a polymer.

Embodiment 10

The method of Embodiment 8 or Embodiment 9, wherein the functionalizedparticles comprise a material selected from the group consisting offunctionalized carbon nanotubes and graphene oxide.

Embodiment 11

The method of any of Embodiments 8 through 10, further comprisingoxidizing a carbon-based material to form the functionalized particles.

Embodiment 12

The method of any of Embodiments 8 through 11, further comprisingreacting a metal of the metal salt with a surface of the functionalizedparticles.

Embodiment 13

The method of any of Embodiments 8 through 12, further comprisingreducing a metal of the metal salt on the surface of the functionalizedparticles.

Embodiment 14

The method of any of Embodiments 8 through 13, further comprisingremoving the solvent from the partially coated particles after formingthe plurality of distinct metal volumes on the surface of thefunctionalized particles.

Embodiment 15

The method of any of Embodiments 8 through 14, wherein the solventcomprises water.

Embodiment 16

The method of any of Embodiments 8 through 15, wherein dispersingfunctionalized particles in a solvent comprises subjecting thefunctionalized particles and the solvent to ultrasonic energy.

Embodiment 17

The method of any of Embodiments 8 through 16, further comprisingforming a powder comprising the partially coated particles.

Embodiment 18

The method of any of Embodiments 8 through 17, wherein thefunctionalized particles comprise functional groups on the carbon-basedmaterial, wherein the metal salt comprises cations, and wherein themethod further comprises adsorbing the cations to the functional groups.

Embodiment 19

The method of any of Embodiments 8 through 18, further comprisingselecting the metal salt to comprise at least one salt selected from thegroup consisting of nitrates, sulfides, sulfates, sulfites, chlorides,bromides, chlorates, perchlorates, and phosphates.

Embodiment 20

The method of Embodiment 18, further comprising selecting the metal saltto comprise at least one salt selected from the group consisting ofnitrates, sulfates, and chlorides.

Embodiment 21

The method of Embodiment 19, further comprising selecting the metal saltto comprise at least one salt selected from the group consisting ofNiCl₂, NiSO₄, CoCl₂, CoSO₄, Cu(NO₃)₂, AgNO₃, and AgCl.

Embodiment 22

A composition of matter comprising a discontinuous coating of metal on asurface of a carbon-based material. The carbon-based material isselected from the group consisting of graphene oxide and functionalizedcarbon nanotubes.

Embodiment 23

The composition of Embodiment 22, wherein the discontinuous coatingcomprises a metal selected from the group consisting of nickel, cobalt,copper, silver, platinum, palladium, chromium, tantalum, antimony, iron,tin, and gold.

Embodiment 24

The composition of Embodiment 23, wherein the discontinuous coatingcomprises a metal selected from the group consisting of nickel, cobalt,copper, and silver.

Embodiment 25

The composition of any of Embodiments 22 through 24, wherein thediscontinuous coating comprises a plurality of thermally insulatedislands of metal over the surface.

Embodiment 26

The composition of any of Embodiments 22 through 25, wherein thecomposition exhibits a thermal conductivity of less than 10⁻² mW/cm K.

Embodiment 27

The composition of any of Embodiments 22 through 26, wherein thecomposition exhibits an electrical conductivity of at least 0.005 S/cm.

Embodiment 28

The composition of any of Embodiments 22 through 27, wherein thecomposition exhibits a Seebeck coefficient of at least 1000 μV/K.

While the present invention has been described herein with respect tocertain illustrated embodiments, those of ordinary skill in the art willrecognize and appreciate that it is not so limited. Rather, manyadditions, deletions, and modifications to the illustrated embodimentsmay be made without departing from the scope of the invention ashereinafter claimed, including legal equivalents thereof. In addition,features from one embodiment may be combined with features of anotherembodiment while still being encompassed within the scope of theinvention as contemplated by the inventors. Further, embodiments of thedisclosure have utility with different and various materials andformulations.

What is claimed is:
 1. A method, comprising: dispersing functionalizedparticles comprising a carbon-based material in a solvent; providing ametal salt in the solvent; and forming a plurality of distinct metalvolumes on a surface of the functionalized particles to form partiallycoated particles, the distinct metal volumes thermally insulated fromother volumes of the plurality.
 2. The method of claim 1, furthercomprising dispersing the partially coated particles within a polymer.3. The method of claim 1, further comprising oxidizing a carbon-basedmaterial to form the functionalized particles.
 4. The method of claim 1,further comprising reacting a metal of the metal salt with a surface ofthe functionalized particles.
 5. The method of claim 1, furthercomprising reducing a metal of the metal salt on the surface of thefunctionalized particles.
 6. The method of claim 1, further comprisingremoving the solvent from the partially coated particles after formingthe plurality of distinct metal volumes on the surface of thefunctionalized particles.
 7. The method of claim 1, wherein dispersingfunctionalized particles in a solvent comprises subjecting thefunctionalized particles and the solvent to ultrasonic energy.
 8. Themethod of claim 1, further comprising forming a powder comprising thepartially coated particles.
 9. The method of claim 1, wherein thefunctionalized particles comprise functional groups on the carbon-basedmaterial, wherein the metal salt comprises cations, and wherein themethod further comprises adsorbing the cations to the functional groups.10. A composition of matter, comprising: a discontinuous coating ofmetal on a surface of a carbon-based material selected from the groupconsisting of graphene oxide and functionalized carbon nanotubes. 11.The composition of claim 10, wherein the discontinuous coating comprisesa metal selected from the group consisting of nickel, cobalt, copper,and silver.
 12. The composition of claim 10, wherein the discontinuouscoating comprises a plurality of thermally insulated islands of metalover the surface.
 13. The composition of claim 10, wherein thecomposition exhibits a thermal conductivity of less than 10⁻² mW/cm·K.14. The composition of claim 10, wherein the composition exhibits anelectrical conductivity of at least 0.005 S/cm.
 15. The composition ofclaim 10, wherein the composition exhibits a Seebeck coefficient of atleast 1000 μV/K.